Fix glitches with struct field aligned indents
Indent correctly after opening square bracket
Allow indenting to align struct fields after curly brace
Indent return type to align with arguments
Add custom group for rust-mode
Add paragraph fill and auto-fill for multi-line comments
Add ERT tests
Fix regression of multi-line statement indents
Cover all cases for padding in paragraph fills as intended
auto merge of #9015 : MicahChalmer/rust/emacs-fixes-round-2, r=nikomatsakis

Here are fixes for more problems mentioned in #8787.  I think I've addressed everything mentioned there except for @nikomatsakis's comment about match/patterns now.  (This also fixes the bug in struct alignment that @pnkfelix mentioned from my earlier pull request #8872.)

The biggest change here is to make fill-paragraph (M-q) and auto-fill-mode work inside different variations of multi-line and doc comments.  Because of the way emacs paragraph fills work (callbacks interacting with global regexp variables that are used in odd ways) there were quite a few edge cases that I had to work around.

The only way I was able to keep it all straight was to create some regression tests.  They use the emacs lisp regression testing tool ERT, and are included as the last commit here.  I added a few tests for indentation as well.  I have not attempted to integrate the tests into the overall rust compiler build process, since I can't imagine anyone would want the compiler build to have a dependency on emacs.  Maybe at some point tools like this get their own repositories?  Just a thought.

One other thought related to the tests: should there be a place to put these types of style samples that isn't specific to one text editor?  Maybe as part of an official rust style guide, but in a form that would allow tools like this to pull out the samples and use them for tests?